My motorhome won't start

At first reading, Motoroamer, I'd think it could be a blockage in the fuel line. It could be air, water, or even old English muck .  Having been stood unused for a while there might be a fair gathering of  Diesel blockers in there !! I'm not sure if this would work, BUT I'd get a friend to give me a good long tow, in gear and ignition on to see if you can force the fuel lines to clear  but there might be a cloud of dirty black smoke for a while.  Good Luck & let us know how you get on  

Do you have an alarm system fitted? Could there be a fault with that which is turning the engine off?

Is there any sign of mice getting into the vehicle? Could they have damaged a cable somewhere? 

Is the exhaust pipe OK? Could something have got inside the exhaust pipe/silencer and died in there?

Presumably other obvious things such as air intake pipes and air filter are OK?

Good luck!

Has your key have a chip and is it still in it as if missing might start then stop

well if he has seen a code that cannot be cleared of low fuel pressure then that's probably the fault as the diesel needs high pressure so the injectors spray a fine mist rather than a dribble. Try cleaning or better replacing the fuel filters. 

If it is a fuel problem you could try heating the engine. Get a load of cardboard boxes and build a wall around the vehicle to seal the underneath as best you can. Put a blanket over the bonnet to block the air intake/radiator grill. If you have an electronic thermometer with a long lead or a remote sensor then put that in the engine compartment so you can monitor the temperature. Put a fan heater under the vehicle and run it for some time. You should see the temperature rise. Pick a warm day to do it, so you are starting from the best possible point. You will probably need to run the fan for at least an hour or two as there is a lot of engine to warm up. Then remove the blanket and the temperature probe and try starting it.

We once started a diesel car using this technique in exceptionally cold (below -20) conditions in the Alps. Only we did not have a fan heater so used 200 candles instead.

Diesel used to gel up many years ago but with the additives used now this is very seldom the case, you used to see on the news hgv drivers lighting fires under the fuel tanks to get the fuel to a liquid state. 

I’ve seen that technique used in Siberia, but starting and cutting out is a classic fuel supply issue. Boat owners are very familiar with ‘diesel bug’ despite additives that may or may not be present in diesel. A tank left half empty in a damp environment with a quantity of supermarket diesel for an extended period can and does become like jelly and clogs up your pump, supply lines and filters. It may be why you’ve got low fuel pressure. Take a look in the fuel filter to check if that’s your problem. I’ve also had similar problems with an intermittent immobiliser fault. 

Like I said in an earlier post check and replace fuel filter. I don't think it really matters as the op hasn't come back with an update. Annoyingly. 

Yes, happens on here a lot. Folks ask for technical support and never heard from or seen again. Discourteous.

I will keep everyone informed on progress!! The last couple of days have been hectic on other things.

Thank you all for your replies. There seem to be a couple of themes and I will talk to our mechanic about these. Interestingly, I also posted on a (french) discussion forum for the Pilote make and replies were similar.

I am particularly interested in the reply about the alarm as the battery in the ignition key has failed.

One or two specifics: 

The fuel filter has been replaced. Even drained the fuel tank, although it is possible there is some residual dirt in the system somewhere.

We've checked cables and haven't found anything untoward. However, we haven't checked the exhaust so I'll add that to the list. The air intake and filters are ok.

I'll discuss heating the engine with our mechanic and see what he thinks!

Once again, thank you all for your suggestions, and I will keep you informed!